1. Field of the Invention
The present invention relates generally to semiconductor wafer manufacturing. More specifically, the present invention relates to control of a chemical mechanical planarization process.
2. Description of the Related Art
In the fabrication of semiconductor devices, planarization operations are often performed on a semiconductor wafer (“wafer”) to provide polishing, buffing, and cleaning effects. Typically, the wafer includes integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Patterned conductive layers are insulated from other conductive layers by a dielectric material. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to increased variations in a surface topography of the wafer. In other applications, metallization line patterns are formed into the dielectric material, and then metal planarization operations are performed to remove excess metallization.
The CMP process is one method for performing wafer planarization. In general, the CMP process involves holding and contacting a rotating wafer against a moving polishing pad under a controlled pressure. CMP systems typically configure the polishing pad on a rotary table or a linear belt.
FIG. 1 is an illustration showing a linear CMP apparatus, in accordance with the prior art. The linear CMP apparatus includes a polishing pad 101 configured to rotate in a direction 105 around rollers 103. A platen 107 is disposed opposite a working surface of the polishing pad 101 to provide backing support to the polishing pad 101 during a CMP operation. A wafer carrier 109 is configured to hold and apply a wafer 111 to the working surface of the polishing pad 101 during the CMP operation. The wafer carrier 109 is capable of rotating in a direction 113 while simultaneously applying the wafer 111 to the polishing pad 101 with an appropriate force as indicated by an arrow 115. An air bearing 117 is utilized between the platen 107 and the polishing pad 101 to facilitate traversal of the polishing pad 101 across the platen 107. A slurry 119 is introduced onto and distributed over the working surface of the polishing pad 101 to facilitate and enhance the CMP operation. Additionally, a conditioner 121 is used to condition the working surface of the polishing pad 101 as it travels in the direction 105.
FIG. 2 is an illustration showing a close-up side view of the linear CMP apparatus, in accordance with the prior art. The wafer carrier 109 is shown applying the wafer 111 to the working surface of the polishing pad 101 with the appropriate force 115. As previously mentioned the polishing pad 101 travels in the direction 105 while the wafer carrier rotates in the direction 113. The slurry 119 is introduced onto the working surface of the polishing pad 101 at a location in front of the wafer carrier 109, relative to the polishing pad 101 movement direction 105. The platen 107 is shown disposed beneath the location at with the wafer 111 is applied to the polishing pad 101. The air bearing 117 is also shown between the platen 107 and the polishing pad 101. The air bearing 117 is formed by introduction of air fluids through a manifold-like structure in the platen 107. A thickness of the air bearing 117 can be changed through adjustment of a platen height. The platen height is typically measured between a top surface of the platen 107 and a fixed reference point. The air bearing 117 properties (i.e., air fluid pressures) and platen height, along with a number of other parameters, are capable of affecting an interface between the wafer 111 and the working surface of the polishing pad 101.
Much of the CMP process is empirically understood but not analytically understood. Due to a lack of analytical understanding and a lack of in situ sensors, real-time control of the CMP process is difficult. The CMP process has traditionally used a statistical surface response method (SRM) to model a relationship between CMP process parameters and associated responses. However, the SRM models are limited in their ability to provide precise, real-time response predictions for complex CMP processes performed under variable environmental conditions.
In view of the foregoing, there is a need for a method that will provide real-time response predictions for CMP processes performed under variable environmental conditions.